1. Field of the Invention
The present invention relates to a method of forming a shaped body from fine particles such as powder, whiskers and short fibers, and more particularly, to a method of forming a shaped body from fine particles by employing a supercritical fluid and a binder which is soluble in the supercritical fluid.
2. Description of the Prior Art
As is described in, for example, an extra issue entitled "Engineering Ceramics" of a periodical named "Nikkei Mechanical" published by Nikkei-McGraw Hill Co. in 1987, it is conventionally known in the field of manufacture of ceramic or metal parts by the sintering to form a shaped body f rom a mixture of a powder material and a fluid binder (fluid in a narrow sense or fluidal material in a broad sense), wherein the mixture is injected into an injection mold or the like, and the molded body is treated by a degreasing process to remove the binder, whereby a shaped body of the powder material remains as a product.
However, in such a conventional powder molding method, since the binder must work as a means to hold the shape of a shaped body as well as a solvent to provide a powder material with a fluidity, a relatively large amount of binder is required due to the requirement for the generation of fluidity, whereby such problems are caused that the molded body has a defective portion like a weld line generated during the injection process, the molded body contracts too much during the degreasing process, and a void or an abnormally contracted portion is generated due to a local concentration of the binder.
Further, in the conventional powder molding method, the mixture of a powder material and a fluid binder must be thoroughly agitated to produce a uniform mixture prior to the injection thereof into the mold. However, it requires a long time to mix fine particles with a fluid binder, generally having a high viscosity, into a uniform mixture.
Still further, in order to remove a large amount of binder from the molded body, the degreasing process, which is a process of heating the molded body at a controlled temperature, requires a long time such as tens of hours or several days, and if such a long time degreasing process is not properly carried out, a cracking, a contraction, or other failure is ready to occur.